Depth of Field in 2.68?
I do not know why, but it seems that using an object as a focal point only works when using an Empty.



Cycles:

(Note that cycles will render with DoF without the need for composite nodes.)



Setting Blades to 3 or more makes it possible to render with a non-circular aperture (this setting refers to the number of "blades" in the camera's aperture)



Blender Internal: